Membranous nephropathy is the most common cause of idiopathic nephrotic syndrome in adults. Recent studies of the pathogenesis of the sub-epithelial glomerular immune deposits that characterize this disease have revealed new mechanisms of glomerular immune deposit formation involving cell surface antigens and have documented the role of the C5b-9 membrane attack complex of complement in mediating renal injury. Understanding these mechanisms may help us understand the pathogenesis of several other immune-mediated diseases and has implications for possible therapeutic interventions in MN.